Non-LTE Luminosity and Abundance Diagnostics of Classical Novae in X-rays

188 Pages·2013·4.68 MB·English

Non-LTE Luminosity and Abundance
Diagnostics of Classical Novae in X-rays
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Peter Nemeth

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Master of Science in Astronomy
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9 A dissertation submitted to
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Florida Institute of Technology
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in partial fulfillment of the requirements
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X Doctor of Philosophy
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Physics
Melbourne, Florida
May 2013
c Copyright 2013 Peter Nemeth
(cid:13)
All Rights Reserved
The author grants permission to make single copies
We the undersigned committee hereby recommends that the attached
document be accepted as fulfilling in part the requirements for the degree of
Doctor of Philosophy in Physics.
"Non-LTE Luminosity and Abundance Diagnostics of Classical Novae in X-rays"
a dissertation by Peter Nemeth
Matthew A. Wood, Ph.D Terry D. Oswalt, Ph.D.
Professor Professor, Department Head
Dept. of Physics and Space Sciences Dept. of Physics and Space Sciences
Academic Advisor Co-Advisor
Stephane Vennes, Ph.D. Hamid K. Rassoul, Ph.D.
Senior Research Scientist Professor, Associate Dean
Astronomický ústav, Ondřejov, Czech Rep. Dept. of Physics and Space Sciences,
Guest Member, Former Advisor College of Sciences
Committee Member
Ming Zhang, Ph.D. Mary L. Sohn, Ph.D.
Professor Professor
Dept. of Physics and Space Sciences Dept. of Chemistry
Committee Member Committee Member
ABSTRACT
Non-LTE Luminosity and Abundance Diagnostics of Classical Novae in X-rays
by
Peter Nemeth
Academic Advisor: Matthew A. Wood, Ph.D.
Classical novae have fundamental importance in astronomy as they are relevant to
both an understanding of individual stellar evolution and to taking proper distance
measurements on galactic and cosmological scales. Also, novae are significant sources
of interstellar material, especially carbon, nitrogen, oxygen and aluminum. These
standard candles are only behind supernovae and γ-ray bursts as the third bright-
est objects in the sky, and the most probable progenitors of the brightest, type Ia
supernovae.
Just after a nova outburst the system enters into the constant bolometric luminos-
ityphaseandthenovamaintainsastablehydrogenburninginthesurfacelayersofthe
white dwarf. As the expanding shell around the nova attenuates, progressively deeper
and hotter layers become visible. At the end of the constant bolometric luminosity
phase, the hottest layers are exposed and novae radiate X-rays.
This work uses the static, plane-parallel model atmosphere code TLUSTY to cal-
culate atmospheric structure, and SYNSPEC to calculate synthetic X-ray spectra of
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novae. It was necessary to incorporate atomic data for the highest ionization stages
forelementsrangingfromhydrogentoironforbothprograms. Atomicdataonenergy
levels, bound-free, bound-bound transitions and natural broadening were taken from
NIST and TOPbase.
Extensive tests revealed the importance of line opacities on atmospheric parame-
ters and on the final spectra. A correlation can be defined between effective temper-
ature and surface gravity. The spectral appearance is not very sensitive to the joint
changes of both. Due to this effect both parameters might be over-estimated with
static models. These tests also showed that N VI and N VII lines are good indicators
of effective temperature.
Model fitting of V4743 Sgr and V2491 Cyg confirmed the anticipated impact of
modeling geometry and stellar wind. Both novae are close to or over the Eddington
limit. Ionization balance and line profiles also indicate this. These results are consi-
tent with previous studies; further and unambiguous details require a comprehensive
update of TLUSTY, what is under way.
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Contents
1 Introduction 1
1.1 The light curve of CNe . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Spectral evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.3 Degeneracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4 The outburst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.5 Supersoft X-ray Sources . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2 Modeling Hot Atmospheres 23
2.1 Model Atmospheres. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2 TLUSTY and SYNSPEC . . . . . . . . . . . . . . . . . . . . . . . . . 29
3 Model Atoms 41
3.1 TOPbase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.2 NIST/ASD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.3 TOPAtom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4 X-ray Modeling of Classical Novae 66
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4.1 Model Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.2 Trends in the model grid . . . . . . . . . . . . . . . . . . . . . . . . . . 93
4.3 Comparison with TMAP . . . . . . . . . . . . . . . . . . . . . . . . . . 109
5 Observations of Classical Novae 111
5.1 Chandra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5.2 XMM-Newton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
5.3 Data Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
5.4 Interstellar absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
5.5 Instrumental resolution. . . . . . . . . . . . . . . . . . . . . . . . . . . 121
5.6 Application to Observations . . . . . . . . . . . . . . . . . . . . . . . . 124
5.6.1 V4743 Sgr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
5.6.2 V2491 Cyg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
6 Conclusions 143
6.1 Future directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Appendices 154
A O VI model atom 155
B Catalog of Galactic CNe with Supersoft Phase 161
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List of Figures
1.1 General light curve of CNe. . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Temporal spectral evolution of V1974 Cyg.. . . . . . . . . . . . . . . . 6
1.3 Maximum magnitude versus rate of decline (MMRD) curve for CNe. . 7
1.4 Spectral evolution of the FeII class. . . . . . . . . . . . . . . . . . . . . 10
1.5 Spectral evolution of the He/N class. . . . . . . . . . . . . . . . . . . . 12
1.6 Fermi-Dirac distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.7 The mass–radius relationship and mass distribution of WDs . . . . . . 17
1.8 Response of WDs to mass accretion. . . . . . . . . . . . . . . . . . . . 21
2.1 The main steps of model atmosphere calculation. . . . . . . . . . . . . 25
3.1 Example for photoionization cross-sections for Mg. . . . . . . . . . . . 54
3.2 Example for photoionization cross-sections for O. . . . . . . . . . . . . 55
3.3 Grotrian diagram for N VII. . . . . . . . . . . . . . . . . . . . . . . . . 60
3.4 Comparison of Fe VI lines in Kurucz database and TOPbase. . . . . . 63
3.5 349 even parity energy levels for Fe VI in TOPbase and NIST. . . . . 65
4.1 LTE – NLTE comparison. . . . . . . . . . . . . . . . . . . . . . . . . . 68
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4.2 Effects of different abundances of carbon on the final spectra. . . . . . 72
4.3 Effects of different abundances of nitrogen on the final spectra. . . . . 73
4.4 Effects of different abundances of neon on the final spectra. . . . . . . 74
4.5 Effects of different abundances of magnesium on the final spectra. . . . 75
4.6 Nova shell abundances. . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.7 Model grid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.8 Final spectrum in LTE and NLTE. . . . . . . . . . . . . . . . . . . . . 81
4.9 Atmospheric structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.10 Ionization fractions for carbon and nitrogen. . . . . . . . . . . . . . . . 83
4.11 Ionization fractions for oxygen, neon and magnesium. . . . . . . . . . . 84
4.12 Ionization fractions for aluminum, silicon and sulfur. . . . . . . . . . . 85
4.13 Ionization fractions for argon, calcium and iron. . . . . . . . . . . . . . 86
4.14 NLTE departure coefficients of ions from H I – C VI. . . . . . . . . . . 88
4.15 NLTE departure coefficients of ions from N V – N VII. . . . . . . . . . 89
4.16 NLTE departure coefficients of ions from O V – O VIII. . . . . . . . . 90
4.17 Departure coefficients of included ions from Ne VII – Ne X. . . . . . . 91
4.18 Departure coefficients of included ions from Mg IX – Mg XII. . . . . . 92
4.19 NLTE-C convergence log. . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.20 NLTE-L convergence log. . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.21 Gravity sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.22 Gravity sequence – structure. . . . . . . . . . . . . . . . . . . . . . . . 97
4.23 PHOENIX flux vs. mass-loss rate. . . . . . . . . . . . . . . . . . . . . 98
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4.24 Temperature sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.25 Temperature sequence – structure. . . . . . . . . . . . . . . . . . . . . 100
4.26 Temperature–gravity sequence. . . . . . . . . . . . . . . . . . . . . . . 101
4.27 Models close to the Eddington limit. . . . . . . . . . . . . . . . . . . . 103
4.28 Effects of higher energy levels. . . . . . . . . . . . . . . . . . . . . . . . 104
4.29 Effects of metallicity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
4.30 Effects of metallicity on atmospheric structure. . . . . . . . . . . . . . 106
4.31 Thickness of atmospheres. . . . . . . . . . . . . . . . . . . . . . . . . . 107
4.32 Radiation pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
4.33 TMAP models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.34 TLUSTY models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.1 The Chandra Observatory. . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.2 The structure of HRMA. . . . . . . . . . . . . . . . . . . . . . . . . . . 114
5.3 The XMM-Newton Observatory. . . . . . . . . . . . . . . . . . . . . . 116
5.4 LETG first order effective area for V4743 Sgr. . . . . . . . . . . . . . 118
5.5 Correction for interstellar absorption. . . . . . . . . . . . . . . . . . . . 120
5.6 RGS spectral resolution. . . . . . . . . . . . . . . . . . . . . . . . . . . 122
5.7 Correction for instrumental resolution. . . . . . . . . . . . . . . . . . 123
5.8 Convolution function for instrumental resolution. . . . . . . . . . . . . 123
5.9 Spectral evolution of V4743 Sgr. . . . . . . . . . . . . . . . . . . . . . 126
5.10 Comparison of LETG and RGS spectra. . . . . . . . . . . . . . . . . . 127
5.11 Model fit for V4743 Sgr. March 19, 2003 . . . . . . . . . . . . . . . . . 130
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